The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Sludge dewatering is a process whereby the liquid and solid portions of sewage and other forms of wastewater are separated. As shown in background FIG. 1, the process for dewatering sludge typically includes four core components, 1) a holding tank, 2) a high-pressure transfer pump, 3) a shear mixer, and 4) dewatering equipment.
The holding tank 1 functions to receive sludge, which is partially treated sewage that contains both solid particles and liquid particles. The size of the tank depends on the volume of material to which the treatment facility processes, and the tank can be made from any number of different materials.
The high-pressure transfer pump 2 functions to receive sludge from the holding tank 1, and discharge the same under pressure downstream to a turbulent mixing valve and then to the dewatering equipment. The most commonly utilized pump for wastewater treatment is a positive displacement pump that typically operates at a pressure of 30-40 psi discharge pressure. One suitable example of a commercially available unit includes a positive displacement progressive cavity pump manufactured by Moyno, Netzsch, and others, for example.
In order to prevent small particles of sludge from passing through the liquid side of the dewatering equipment, polymers are typically added to the sludge to bind the waste particles together. This polymer injection process is performed on the discharge side of the pump and is typically accomplished through the use of a high shear mixing pattern wherein violent agitation of the polymer and slurry occur in the shortest time possible.
In order to operate at peak capacity, shear mixers typically require the above noted 30 psi, to thoroughly mix the materials, and thus create an output of approximately 80-600 gallons per minute of sheared mixed polymer/sludge material that is then fed to the dewatering equipment.
The dewatering equipment functions to receive the sheared mixed polymer/sludge material and separate the solids from the liquids. One of the most commonly utilized types of dewatering equipment includes a filter press system that utilizes pressure and porous membrane belts filters to perform the separation process. One suitable example of a commercially available unit includes the Belt Filter Press from Ashbrook Simon-Hartley, Inc., for example.
Although this process has been utilized for many years, there are several inefficiencies in layout and implementation of such systems. For example, the use of a downstream mixer to break up/shear the sludge so that it can be mixed with the polymer is counterproductive to the process performed by the dewatering equipment, as this requires the dewatering equipment to attempt to reconnect/compact the solid sludge particles back together when performing the separation process.
Moreover, by mixing the polymer with the sludge and then shearing the composition, the mixer functions to break up the long chain molecules of the polymer, thus requiring a relatively large amount of polymer to be used.
Finally, the energy utilized by the high shear mixer requires the pump to work significantly harder in terms of power and pressure to supply the material to the dewatering equipment, as noted above.
Accordingly, through extensive research and development, the inventors of the present invention have created an improved system for providing a homogeneous polymer-sludge composition to dewatering equipment, that reduces the overall number of components, and reduces material and energy costs. The manner by which will become more apparent in the description which follows, particularly when read in conjunction with the accompanying drawings.